1. Field of the Invention
The present invention is generally directed to the extraction of chemical compounds from a sample and, more particularly, to a method of separating families of organic compounds present in a liquid sample.
2. Description of the Prior Art
Samples consisting of a liquid, in which chemical compounds, such as organic compounds, are dissolved are often processed to extract different groups of compounds which are present in the sample. One process is often referred to as liquid-liquid extraction. In this process the extraction is achieved by the addition of a suitable extracting solvent (or solvents) which is generally immiscible in the liquid of the original sample and by causing the desired compounds to become separated from the sample liquid and become dissolved in the extracting solvent. Extraction is caused by one of two phenomena: (a) Physical solution; and (b) chemical reaction and solution.
In the former, extraction takes place because the desired compounds are initially more soluble in the extracting solvent than in the liquid of the original sample hereinafter referred to as the sample liquid. In other words, the partition coefficients of the compounds are in favor of the extracting solvent. Thus, when the latter is introduced into the sample the desired compounds become dissolved in it. In the extraction based on chemical reaction and solution, a reagent (or reagents) is introduced with the extracting solvent, which upon contact with the compounds of interest forms derivatives which are more soluble in the extracting solvent than in the sample liquid.
These techniques and phenomena are well known by those familiar with the art. For example, in the field of toxicology, blood or urine samples which are aqeuous liquids are processed by means of extracting organic solvents, to determine the presence of groups or individual drugs (organic compounds) in the samples. With the ever increasing number of samples being processed, the prior art liquid-liquid extraction techniques, through relatively simple, have been found to be too time-consuming, requiring the use of different devices and containers, and the attention of experienced technicians, all of which add to the sample processing cost.
Typically, present state of the art liquid-liquid extraction consists primarily of introducing the sample, e.g., blood into a phase separator or vessel to which an appropriate solvent with reagents are added. Generally, the volume of solvent is much larger than the sample volume. The phase separator is then shaken for a period of time. The sample, due to the turbulent action upon it and the fact that its liquid is immiscible with the solvent, tends to break up into droplets, which travel through the larger volume of the solvent. This action produces surface to surface contact between the sample liquid droplets and the solvent. As a result of this contact the desired compounds, whose partition coefficients were adjusted by the reagents to favor the solvent, become separated from the sample liquid and become dissolved in the solvent. Thus, a mass transfer of the desired compounds takes place from the original sample liquid to the solvent. Clearly, the greater the contact area between the sample liquid and the solvent, the faster and more efficient is the extraction. This is achieved by insuring a sufficiently long shaking period.
Thereafter, the solvent, now containing the desired compounds, is separated from the rest of the sample by passing the phase separator content through a filter. The separated compounds which are dissolved in the solvent are often referred to as the extract or solutes. If an emulsion is created as a result of the shaking, centrifugation is required to remove the emulsion. If more than one extract from a single sample is desired, i.e., if more than one group or family of the compounds in the sample are to be extracted therefrom, after removing the first extract, the procedure must be repeated. This is done by adding new solvents with other reagents, suitable for the extraction of the second extract, to the remaining sample in a second phase separator or to a new quantity of the same sample. Thereafter, the shaking, filtering and centrifugation are repeated.
This procedure, which is well known by those familiar with the art, is quite lengthy and requires nearly continuous operator performance and attention, and therefore it is quite costly. Furthermore, it requires a considerable amount of equipment such as a centrifuge, drying apparatus and elements, such as the filters, which are discarded after each filtration step.
In another technique for extracting an extract from an aqueous liquid sample, i.e., a sample consisting of an aqueous liquid in which compounds are dissolved, e.g., deproteinized blood or urine, a column containing a non-ionic resin is used. The resin attracts only non-ionic compounds which pass through it. In use the aqueous liquid sample pH is first adjusted and, thereafter, it is passed through the column. The non-ionic resin attracts the non-ionic compounds of the sample and the rest of the sample, which is not attracted, passes out of the column. To remove any residue the column is washed and only thereafter is the extract, comprising the attracted non-ionic compounds, eluted by passing a solvent through the column. Thus, this technique also requires a substantial number of steps. To extract a second extract from the liquid sample its pH must be adjusted to a different value and the above steps must be repeated in the same or another column.
Since the number of extractions which are performed in various laboratories, such as those engaged in clinical chemistry or in forensic studies is very large, a need exists for a new device for and method of extracting extracts from samples which do not require the above procedures to be followed. Basically, a need exists for a new method to simplify the extraction of families of chemical compounds, hereinafter referred to as extracts or solutes, from liquid samples.